U.S. patent number 4,490,112 [Application Number 06/414,189] was granted by the patent office on 1984-12-25 for orthodontic system and method.
This patent grant is currently assigned to Kabushiki Kaisha Suwa Seikosha, Takehiko Disaku. Invention is credited to Takehiko Daisaku, Yoshihide Suda, Susumu Tanaka.
United States Patent |
4,490,112 |
Tanaka , et al. |
December 25, 1984 |
Orthodontic system and method
Abstract
An orthodontic system including an ultraelastic archwire having
a transformation temperature of normal body temperature of about
37.degree. C. is provided. Only a small load is applied to the
teeth when the orthodontic system is disposed in a patient's mouth.
An increased load is applied to the teeth only when the temperature
in the mouth is increased by placing a material having a higher
than body temperature in the mouth. As a result, the temperature in
the patient's mouth can be controlled without inflicting pain
during natural every day actions. The orthodontic effect is
available intermittently by raising the mouth temperature for
producing higher stress or load which serves to move the teeth
orthodontically. The ultaelastic alloy is preferably Ni-Ti alloy
containing at least about 50.5 atomic percent of nickel and
preferably about 50.7 atomic percent.
Inventors: |
Tanaka; Susumu (Suwa,
JP), Daisaku; Takehiko (Kodaira, JP), Suda;
Yoshihide (Tokyo, JP) |
Assignee: |
Kabushiki Kaisha Suwa Seikosha
(Tokyo, JP)
Takehiko Disaku (Tokyo, JP)
|
Family
ID: |
23640341 |
Appl.
No.: |
06/414,189 |
Filed: |
September 2, 1982 |
Current U.S.
Class: |
433/20 |
Current CPC
Class: |
A61C
7/00 (20130101); A61C 7/20 (20130101); A61C
2201/007 (20130101) |
Current International
Class: |
A61C
7/00 (20060101); A61C 7/20 (20060101); A61C
007/00 () |
Field of
Search: |
;433/20 ;428/960 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Effect of Low Temperature Phase Changes on Mechanical Properties of
Alloys Near _Composition T.N., by Buehler et al., Journal of
Applied Physics vol. 34 No. 5, May 1961. .
"Metals That Remember" by Hansen, Science 81, Jun. 81, pp.
44-47..
|
Primary Examiner: Peshock; Robert
Attorney, Agent or Firm: Blum, Kaplan, Friedman, Silberman
& Beran
Claims
What is claimed is:
1. An orthodontic arch wire member comprising an alloy of the
thermoelastic-type which undergoes a martensitic transformation
caused by stress at a temperature above normal body temperature for
selectively applying a variable orthodontic load in response to the
difference between normal body temperature and a temperature in the
mouth above normal body temperature caused by placing a
temperature-affecting material having a temperature above normal
body temperature in the mouth.
2. The orthodontic member of claim 1, wherein said alloy is formed
of principally an intermetallic compound of nickel and
titanium.
3. The orthodontic member of claim 2, wherein the inverse
martensitic transformation of the Ni-Ti alloy terminates at a
temperature below normal body temperature.
4. The orthodontic member of claim 3, wherein the Ni-Ti alloy
comprises at least about 50.5 atomic percent nickel.
5. The orthodontic member of claim 5 having the shape of a wire
with a diameter of about 0.4 mm before polishing
6. The orthodontic member of claim 3, wherein the Ni-Ti alloy
comprises between about 50.5 and 51.0 atomic percent nickel with
the balance titanium.
7. The orthodontic member of claim 3, wherein the Ni-Ti alloy
comprises about 50.7 atomic percent nickel with the balance
titanium.
8. The orthodontic member of claim 4, wherein a portion of the
nickel is replaced by at least one of copper, iron and cobalt.
9. An orthodontic arch wire system comprising an orthodontic member
comprising an orthodontic member comprising a thermoelastic-type
alloy which undergoes a martensitic transformation caused by stress
at a temperature above normal body temperature for selectively
applying a variable orthodontic load to malaligned teeth in
response to a temperature difference between normal body
temperature and a temperature in the mouth above normal body
temperature caused by placing a temperature-affecting material
having a temperature above normal body temperature in the
mouth.
10. An orthodontic method for the orthodontic arch wire movement of
teeth comprising coupling to the teeth to be moved an orthodontic
member which undergoes a martensitic transformation for select
applying a variable orthodontic load in response to the difference
between normal body temperature and a temperature caused by placing
a temperature-affecting material in the mouth and selectively
raising the temperature of the mouth to above normal body
temperature to increase the orthodontic load applied to said
teeth.
11. The orthodontic member of claim 1, wherein the inverse
martensitic transformation of Ni-Ti alloy terminates at a
temperature above normal body temperature.
Description
BACKGROUND OF THE INVENTION
This invention relates to a novel orthodontic system and
orthodontic method for the orthodontic movement of malaligned teeth
and more particularly to a system utilizing an ultraelastic
material which applies a variable orthodontic load in response to
temperature change.
Conventional systems for the orthodontic movement of teeth have
usually been based on the elasticity of a metal wire. A load
created by bending a metal wire is applied to the tooth to be
corrected in order to move it in the direction of the load. Such
conventional systems utilize orthodontic metal wires formed from
stainless steel, a Co-Cr based alloy or an intensly worked Ni-Ti
alloy. The elasticity of these wires is represented by the
proportional elastic limit of the metal or alloy involved. The
Ni-Ti alloy has a higher proportional elastic limit than the
stainless steel or other alloys. However, the Ni-Ti alloy does not
exhibit elongation exceeding about 2% in a tensile test. The
stainless steel and other alloys show elongation which is less than
1%. Thus, if the wire is bent or pulled beyond its proportional
elastic limits it undergoes plastic deformation. Excessive
deformation is unpredictable in the conventional wires. This small
proportional elastic limit means that the orthodontic effect
obtained is relatively small.
The elasticity of the conventionally utilized metallic materials is
an inherent property thereof which is difficult to modify by heat
treatment or otherwise. Specifically, it is not possible to heat
treat an intensively worked Ni-Ti alloy, since heat treatment
reduces by about one-half the proportional elastic limits which has
been obtained by the intense working. U.S. Pat. No. 4,037,324
utilizes one such alloy wherein a stoichiometric alloy of Ni and
Ti, specifically the atomic ratio of Ni to Ti is 1:1 . An
orthodontic system based on this alloy presents practical problems
when utilized in that a patient undergoes intense pain, often with
the dental periosteum suffering from interruption in blood
circulation. This occurs because the transformation temperature
(which is the lowest temperature wherein the ultraelastic effect
occurs) is 26.7.degree. to 32.2.degree. C., a temperature lower
than normal body temperature. Thus, the large load is applied
continually to the teeth at all times that the orthodontic system
is disposed in the patient's mouth. This system based on the
stoichiometric alloy of Ni and Ti is not fully satisfactory from
the point of view of the patient's comfort.
Accordingly, it would be desirable to provide an orthodontic system
which overcomes the shortcomings of the prior art systems. Such a
system would apply a very small load to the teeth when the
orthodontic system is disposed in a patient's mouth, and only apply
an increase load when the temperature in the mouth is increased by
taking in a material having a temperature above body
temperature.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, an
orthodontic system including an orthodontic member which applies
variable orthodontic load in response to a difference between
normal body temperature and the temperature prevailing upon
placement of a temperature affecting material in the mouth is
provided. The orthodontic member is a Ni-Ti alloy containing about
50.5 to 51.0 atomic percent nickel with the balance titanium having
a transformation temperature of about 37.degree. C. or normal body
temperature. This permits applying a very small load to the teeth
when the orthodontic system is installed in a patient's mouth and
increasing the orthodontic load to the teeth when the temperature
in the mouth is increased by taking in a high temperature material,
such as hot water. Utilizing a orthodontic system whose
transformation temperature is about normal body temperature permits
intermittently varying the orthodontic load applied to the teeth to
promote orthodontic movement of the teeth more effectively.
Preferably the orthodontic member in accordance with the invention
is formed from a Ni-Ti alloy containing 50.7 atomic percent
nickel.
Accordingly, it is an object of the invention to provide an
improved orthodontic system.
It is another object of the invention to provide an improved
orthodontic system for intermittently varying the load applied to
promote orthodontic movement of teeth more effectively.
It is a further object of the invention to provide an improved
orthodontic system wherein intermittently varying orthodontic loads
are applied in response to the temperature of the patient's
mouth.
Still a further object of the invention is to provide an improved
orthodontic member for applying a varying orthodontic load in
response to the temperature of the patient's mouth.
Yet another object of the invention is to provide an improved
orthodontic system including an orthodontic member of a Ni-Ti
alloy.
Yet a further object of the invention is to provide an improved
orthodontic system wherein the orthodontic member is a Ni-Ti alloy
containing from about 50.5 to 51.0 atomic percent nickel.
Another object of the invention is to provide an improved method of
promoting orthodontic movement of teeth.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the several steps and the
relation of one or more of such steps with respect to each of the
others, and the apparatus embodying features of construction,
combination of elements and arrangement of parts which are adapted
to effect such steps, all as exemplified in the following detailed
disclosure, and the scope of the invention will be indicated in the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to
the following description taken in connection with the accompanying
drawings, in which:
FIG. 1 are graphs illustrating the load-strain characteristics
obtained from tensile test of an ultraelastic wire utilized in an
orthodontic device prepared in accordance with the invention;
FIG. 2 are graphs showing the load-strain characteristics obtained
from bending tests of the same wire utilized in FIG. 1; and
FIG. 3 is a schematic view illustrating the principle of the
orthodontic movement of teeth utilizing the ultraelastic wire in
accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The physiological aspects of the orthodontic system constructed and
arranged in accordance with the invention will now be described.
Generally, a substantially constant orthodontic load has been
applied in orthodontic systems. However, in accordance with the
invention, an intermittently varying load is applied to promote
orthodontic movement of the teeth effectively. More specifically,
the orthodontic movement of the teeth in accordance with the
invention utilizes a variation in the temperature in the mouth. The
orthodontic member applies an orthodontic load which varies in
response to a difference in the temperature of the mouth between
normal body temperature (37.degree. C.) and the higher or lower
temperature wherein a high temperature effecting material, such as
hot water or food, or a cold material, such as cold water or ice
has been placed in the mouth. The orthondontic load increases in
response to an increase in the temperature of the mouth. The
orthodontic system in accordance with the invention facilitates
effective orthodontic treatment, since the patient takes at least
some of such temperature effecting materials every day.
Additionally, such materials can be taken consciously so as to
apply the orthodontic load selectively.
The application of an intermittently varying load to the human body
is physiologically more effective, and can complete orthodontic
treatment more quickly than application of a constant load. In
accordance with the invention, it is sufficient normally to
maintain a light orthodontic load. In fact, no load need be
maintained when the mouth is at normal body temperature. A maximum
load can be selected to be applied only when a certain temperature
affecting material is placed in the mouth. Thus, it is possible to
avoid pain or discomfort on the part of the patient to a great
extent. A light load which is normally maintained is at a level
which discomfort is negligible for the patient and will remove any
mental discomfort during the time of orthodontic treatment which
usually extends over an appreciable period of time.
Previously it was believed that maximum orthodontic force must be
applied for moving the teeth. However, in accordance with the
invention the orthodontic load is applied and released to move the
teeth intermittently. A compressed region is formed on the dental
periosteum on the side of the tooth in the direction in which it is
being moved and formation of osteoclasts causes absorption on the
alveolar wall. A pulled zone is formed on the dental periosteum on
the opposing side. The activity of bone-forming cells results in
addition on the opposite alveolar wall.
When the orthodontic system in accordance with the invention is
utilized, the dental periosteum does not suffer from any
interruption in blood circulation. This is due to the fact that
maximum load bears only temporarily on the tooth and is maintained
at a comfortable level otherwise. Additionally, the variable load
promotes formation of the osteoclasts and bone-forming cells for
enhancing the progress of the orthodontic treatment. Having
discussed the advantages of the orthodontic system in accordance
with the invention, a method for orthodontic treatment may be
carried out by utilizing an orthodontic device which will not be
described.
The orthodontic system in accordance with the invention is formed
utilizing a material exhibiting ultraelasticity, for example an
utlraelastic Ni-Ti alloy. Ultraelasticity is a property, entirely
different from the proportional elastic limit of conventionally
available metallic materials. An ultraelastic material returns to
its original shape upon removal of the deforming load even if
deformation of about 8% is imposed during a tensile test. This high
elastic deformability permits bending or pulling required for any
orthodontic purposes.
When the ambient temperature of the orthodontic device changes, the
device applies a load which varies in response to the temperature
change in such a fashion that the load increases with an increase
in temperature. This is due to the fact that in the range of
ultraelasticity, the stress (or load) is substantially constant,
and is proportional to the temperature. The variation in stress (or
load) with a change in temperature is a feature not found in other
materials. This feature enables variation in orthodontic load with
a temperature variation selectively caused by the temperature of a
material placed in the mouth.
In order to provide an orthodontic device having these desired
properties, it is not sufficient merely to utilize an ultraelastic
Ni-Ti alloy, but it is necessary to select an appropriate alloy
composition. Additionally, it is necessary to select appropriate
conditions for the preparation of the orthodontic device by
appropriate heat treatment. The utlimate properties of the
orthodontic device can also vary with the shape of the device, for
example the diameter of the wire or the cross-section. When these
factors are appropriately considered with respect to one another,
it is possible to provide the properties required for varying
orthodontic purposes.
The orthodontic system in accordance with the invention will now be
described in greater detail. Examples of ultraelastic metallic
materials which can be utilized in accordance with the invention
include various alloys. Such alloys may include intermetallic
compounds of nickel and titanium, and also may be alloys of Cu and
Zn; Cu, Zn and X, wherein X is Si, Sn, Al, etc.; Cu, Al and Ni; Au
and Cd; Ag and Cd; Ni and Al; Cu, Au and Zn or Cu and Sn. The
alloys are of the "thermoelastic" type having a superlattice and
which undergo a martensitic transformation. Their ultraelasticity
is derived from the martensitic transformation caused by stress at
a temperature range above the martensitic transformation
temperature and the inverse transformation thereof. There is only a
small degree of hysteresis in the normal and reverse transformation
between the austenite and the martensite; therefore, these alloys
undergo crystallographically reversible transformation.
Crystallographic reversibility means not only the restorability of
the austenitic structure, but also of its original crystal
orientation.
An ultraelastic alloy of nickel and titanium is polycrystalline.
Thus, it is an optimum material for orthodontic devices, since it
has excellent properties, including corrosion resistance. As a
result of recent research, not only are Ni-Ti alloys available, but
it possible to obtain alloys containing copper, iron or cobalt
instead of the nickel and which have a controlled transformation
temperature, a low degree of hysteresis and a small difference in
ultraelasticity when a load is applied and when the load is
removed.
The Ni-Ti alloy which contains at least 50.5 atomic percent nickel
exhibits ultraelasticity of a temperature of about 37.degree. C.,
which corresponds to the normal mouth or body temperature. An
orthodontic member in accordance with the invention is formed
preferably from an Ni-Ti alloy containing somewhat more nickel,
namely about 50.7 atomic percent nickel was formed as follows.
A raw material containing 50.7 atomic percent nickel, with the
balance being titanium, was melted at a high frequency vacuum
furnace and the molten material was poured into a copper mold to
form an ingot. The ingot was forged into a billet and the billet
was diedrawn into a wire having a diameter of 0.4 mm. The wire rod
was annealed during the drawing operation so that any further
drawing thereof might be performed smoothly. The wire was polished
to have a mirror surface and a final diameter of 0.37 mm. The wire
was heat treated in a vacuum furnace to remove any strain created
during the drawing operation and obtain ultraelasticity. The wire
was heat treated under the following conditions:
Temperature: 700.degree. C.;
Treating time: One hour;
Cooling: The wire was left in the furnace to cool slowly.
The properties of the heat treated wire were as follows:
______________________________________ Temperature at which
martensitic -40.degree. C. transformation begins: Temperature at
which inverse 5.degree. C. martensitic transformation ends:
Load-strain characteristics See FIG. 1 found from a tensile test:
Load-strain characteristics See FIG. 2. -found from a bending
______________________________________ test:
Referring now to FIG. 1, the load-strain characteristics of the
wire are shown. The characteristics of the wire under load are
shown by the solid line curves and the characteristics after
removal of the load by the broken lines. Deformation and
restoration of the wire took place at a fixed load both when the
load was applied and removed. This is the feature called
"ultraelasticity." The lower curve represents test results obtained
at ordinary body temperatures of 37.degree. C. The upper curve
illustrates the results obtained at a temperature of 60.degree. C.
simulating the presence of a hot substance in the mouth. The graph
indicates that a higher load for the same amount of deformation is
obtained at the higher temperature, the same phenomenon occuring
both under low and upon removal of the load.
FIG. 2 illustrates the bending characteristics of a 10 mm long wire
secured at one end with the load applied to the other end. The
curves indicate that a greater load occurs at 60.degree. C. than at
37.degree. C. for the same amount of deformation. This tendency
corresponds to that obtained in the tensile tests. FIG. 2 also
shows that the deformation of the wire beyond a certain level
proceeds at a constant load. This feature is called
"ultraelasticity in bending.".
The results of both the tensile and bending tests demonstrate that
the orthodontic device in accordance with the invention undergoes
deformation or restoration at a certain load depending upon the
ambient temperature. This is true whether under load or after
removal of the load. The load depends upon the martensitic
transformation temperature of the material. More specifically, the
ultraelastic load upon application thereof depends on the
temperature at which the alloy begins martensitic transformation
(Ms point), while the ultraelastic load upon removal thereof
depends upon the temperature at which the alloy finishes inverse
martensitic transformation (Af point).
In view of these characteristics it is necessary that the
orthodontic device in accordacne with the invention be formed from
a material capable of undergoing inverse martensitic transformation
at a temperature below normal mouth temperature of 37.degree. C.
This is necessary in order to retain the ultraelasticity at a
temperature of at least 37.degree. C. It is, thus, necessary to
employ an alloy containing between about 50.5 to 51.0 atomic
percent, or preferably 50.7 atomic percent, of nickel the balance
being titanium.
The transformation temperature of an alloy may be affected by its
heat treatment conditions. It is, therefore, necessary to
anticipate that the orthodontic device will be heat treated when it
is installed, particularly by an orthodontist. Although it is
desirable to employ a heat treating furnace wherein the temperature
can be controlled, an orthodontist usually uses a more simple
apparatus. The orthodontist will heat treat the wire by applying an
electric current thereto and utilizing the heat generated by the
electric resistence of the wire. A wire treated by this method
cools quickly and tends to have a lower transformation temperature
than that of a wire cooled slowly in a heat treating furnace.
In view of this, if a wire provided to an orthodontist can furnish
inverse martensitic transformation at a temperature of 37.degree.
C. corresponding to normal body temperature, subsequent heat
treatment lowers its transformation temperature to a level below
37.degree. C. and insures the satisfactory elasticity of the device
at normal body temperatures. Thus, it is possible to preset a
somewhat higher transformation temperature to provide for any
further reduction thereof brought about by the faster cooling rate
upon installation.
An orthodontic device utilizing a wire formed in accordance with
the invention will now be described by way of an example.
An ultraelastic wire is prepared in a straight form so that it may
be utilized for a variety of purposes. It is, of course, possible
to prepare a wire in the shape of an arch like an array of teeth.
An easier method for obtaining a more precise shape to place an
ultraelastic wire in a mold having a desired shape and heat treat
the same. This method facilitates realization of very complicated
shapes. An orthodontist may heat treat the wire at a temperature of
200.degree. C. or higher.
Referring now to FIG. 3, an ultraelastic archwire 1 is fastened to
a tooth 2 to be moved, and a first normal tooth 3 and a second
normal tooth 4 on both sides thereof. Wire 1 may be fastened to the
teeth by following any conventional method in the art. For example,
a bracket 5 can be bonded directly to each tooth, or welded to a
metal ring fitted over a tooth. In FIG. 3, the pair of solid
arcuate lines show the position of wire 1 fastened only to normal
teeth 3 and 4, while the broken lines show the position of wire 1
fastened to the malaligned tooth 2 also. Archwire 1 is placed under
bending and tensile stresses along an array of teeth 3, 2 and 4 and
a force (or load) which urges wire 1 to recover its original shape
bears on tooth 2 in the direction of the arrow.
Tooth 2 is moved gradually by the load applied thereto and aligned
correctly. Under normal circumstances, the temperature in the mouth
is equal to the normal body temperature of 37.degree. C., and
therefore, ultraelastic wire 1 in accordance with the invention
produces only a slight stress or load. However, once hot tea or
coffee is taken into the mouth, or during a meal, the temperature
of the wire is raised temporarily to a higher temperature in the
range of, for example, 50.degree. C. to 60.degree. C. This elevated
temperature produces a higher stress or load which serves to move
tooth 2 orthdontically. If on the other hand, cold water, ice or
any other substance having a lower temperature than the normal
mouth temperature is taken in, wire 1 produces a smaller stress or
load which at times may be zero. Intermittent application of the
load as hereinabove described is quite effective
orthodontically.
The orthodontic treatment of teeth with a device prepared in
accordance with the invention is initiated if a hot or cold
substance is placed in the mouth repeatedly. A correctly aligned
array of teeth can be obtained usually after one to several months
of such treatment. Although a simple example has been described,
the invention is equally applicable to any more complicated
orthodontic treatment of teeth. The use of an ultraelastic wire is
even more effective for such complicated treatments. For example,
the high elastic deformability of the ultraelastic wire in
accordance with the invention enables more effective simultaneous
correction of a plurality of malaligned teeth which have to be
moved to different degrees.
It is obvious fom the foregoing description that the orthodontic
system and orthodontic method in accordance with the invention
provides a novel and effective means to correct the positioning of
a malaligned tooth or teeth selectively during very natural every
day actions, such as drinking hot or cold water and eating of
meals, while relieving the patient of any orthodontic pain. The
orthodontic device in accordance with the invention provides a host
of advantages derived from full utilization of the ultraelasticity
obtainable from an alloy prepared in accordance with the
invention.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and since certain changes may be made in carrying out the
above method and in the construction set forth without departing
from the spirit and scope of the invention, it is intended that all
matter contained in the above description and shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described, and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
Particularly it is to be understood that in said claims, ingredints
or compounds recited in the singular are intended to include
compatible mixtures of such ingredients wherever the sense
permits.
* * * * *